Urinary Neutrophil Gelatinase–Associated Lipocalin (NGAL) Distinguishes Sustained From Transient Acute Kidney Injury After General Surgery

INTRODUCTION: This prospective study tests the hypothesis that after general surgery urinary neutrophil gelatinase–associated lipocalin (NGAL) can distinguish between sustained acute kidney injury (AKI), typical of nephron damage, and transient AKI, commonly seen with hemodynamic variation and prerenal azotemia. METHODS: Urine was collected in 510 patients within 2 to 3 hours after general surgery, and urinary NGAL was determined using enzyme-linked immunosorbent assay. Patients who met AKIN stage 1 criteria of AKI were subclassified into those with sustained AKI (serum creatinine elevation for at least 3 days) and those with transient AKI (serum creatinine elevation for less than 3 days). RESULTS: Seventeen of 510 patients (3.3%) met the stage 1 AKIN criteria within 48 hours of surgery. Elevations in serum creatinine were sustained in 9 and transient in 8 patients. Urinary NGAL was significantly elevated only in patients with sustained AKI (204.8 ± 411.9 ng/dl); patients with transient AKI had urinary NGAL that was indistinguishable from that of patients who did not meet AKIN criteria at all (30.8 ± 36.5 ng/dl vs. 31.9 ± 113 ng/dl). The area under the curve of the receiver operating characteristic curve of urinary NGAL to predict sustained AKI was 0.85 (95% confidence interval: 0.773–0.929, P < 0.001). DISCUSSION: Urinary NGAL levels measured 2 to 3 hours after surgery were able to distinguish the kinetics of creatinine (sustained AKI vs. transient AKI) over the subsequent week. Transient AKI is an easily reversible state that is likely not associated with substantial tubular injury and therefore NGAL release. Using AKIN criteria, both transient and sustained AKI are classified as AKI even though our data demonstrate that they are possibly different entities.